Wall covering undergoes numerous physical changes as it is transformed from dry roll form, applied to a wall surface, and ultimately removed. Generally, wall covering is unrolled in a dry state, and in preparation for hanging on a wall surface is wetted with paste or submersed in water to activate a prepaste. The wall covering is then bookfolded to enable it to either shrink or expand and allow the wall covering adhesive to "setup". The wall covering is then applied to the wall by stretching and pulling it into position, and then smoothing the same with tools and rollers to evacuate air bubbles and eliminate seams. At this stage, the wall covering is allowed to dry on the wall surface, hopefully without stretching or shrinking. At some time in the future, the wall covering may be stripped from the wall surface, usually a difficult task without causing damage.
Wall coverings must meet several design criteria. The decorative printing should be resistant to UV light, as long term exposure causes undesirable fading. The surface should be washable to enable cleaning everyday spills and inevitable dirt accumulation over long periods of time. The material should be adapted to prevent the formation of bacteria and mold. The texture and surface of the material should be aesthetically pleasing, and the material if so desired should be embossable and paintable. Finally, the materials employed in the process should be environmentally safe and meet ASTM-84 flame certification standards.
Paper wall covering is normally "wet" printed, either by inexpensive single color printing or highly complex and relatively expensive multiple color printing. It has been the dominant wall covering material, and still remains popular. However, due to several shortcomings it has given away a significant market share to vinyl supported wall coverings. Paper has the disadvantage of low physical durability, requires careful preparation of the wall surface before hanging, and is susceptible to expansion and shrinkage during hanging. Paper is usually not washable, susceptible to cracking, and not easily strippable when the wall covering is to be removed.
Another common wall covering is vinyl supported, and utilizes high volume "wet" printing and embossing processing with in-line rotor screen and gravure printing. Vinyl supported wall covering is physically durable and washable, but must be backed by a paper, scrim or non-woven material which adds to the cost and complexity of manufacturing. Furthermore, vinyl is difficult to apply to wall surfaces and requires significant drying time. It also is a good host for mold and bacteria due to its low permeability, and requires a large capital investment for processing.
Non-woven material is commonly used as a backing material, and has lowered manufacturing costs for vinyl supported wall coverings. Non-woven backing improves the physical characteristics of vinyl supported wall covering and increases its strippability, adhesion, and surface appearance. However, without a vinyl plastisol coating or a vinyl laminated surface, non-woven materials are not aesthetically suitable for wall covering. The porous nature and uneven texture of non-woven materials generally causes "bleed through" and dimpling, both considered undesirable results in printing. In addition, without a vinyl plastisol or vinyl laminated surface, non-woven materials are not washable since their low surface durability results in excessive piling.
In summary, printed wall covering paper has acceptable aesthetic qualities with low capital investment, but suffers low physical durability and poor strippability. Vinyl has superior aesthetic qualities for printing and strong physical durability, but requires a supporting material, thereby increasing manufacturing complexity and costs. Non-woven materials used as a backing improve vinyl supported wall covering in adhesion, strippability, and embossing, but are not independently suitable for wall covering without a vinyl plastisol coating or vinyl laminated surface.